1. Field of the Invention
The present invention relates to a method for manufacturing a thermally-assisted magnetic head, which irradiates near-field light to a magnetic recording medium, reduces coercive force of the magnetic recording medium, and records information.
2. Description of the Related Art
In recent years, for magnetic recording devices such as magnetic disk devices, etc., performance improvements of a magnetic head and a magnetic recording medium are demanded in association with high recording density. As the magnetic head, a composite-type magnetic head, in which a reproducing head that has a magneto resistive effect element (MR element) for reading and a magnetic recording head that has an inductive-type electromagnetic transducer element (a magnetic recording element) for writing are laminated on a substrate, has widely been utilized. In the magnetic disk devices, the magnetic head flies slightly above a surface of the magnetic recording medium.
The magnetic recording medium is a discontinuous medium on which magnetic microparticles gather. Each of the magnetic microparticles has a single magnetic domain structure. Of the magnetic recording medium, one recording bit is configured with a plurality of the magnetic microparticles. In order to increase the recording density, the asperity of a boundary of adjacent recording bits needs to be small. For this, the size of the magnetic microparticles needs to be small. However, when the size of the magnetic microparticles is small, thermal stability of the magnetization of the magnetic microparticles is also decreased due to the decrease in the volume of the magnetic microparticles. In order to solve this problem, increasing the anisotropy energy of the magnetic microparticles is effective. However, when the anisotropy energy of the magnetic microparticles is increased, the coercive force of the magnetic recording medium is also increased. As a result, it becomes difficult to record information using a conventional magnetic recording head. The conventional magnetic recording head has such a drawback, and this is a large obstacle to achieving an increase in the recording density.
As a method to solve this problem, a so-called thermally-assisted magnetic recording method has been proposed. In this method, a magnetic recording medium that has a large coercive force is utilized. The magnetic field and heat are simultaneously added to a portion of the magnetic recording medium where information is recorded at the time of recording the information. Using this method, the information is recorded under a state where the temperature is increased and the coercive force is decreased in the information record part.
For a thermally-assisted magnetic recording, it is common to utilize a laser light source for heating the magnetic recording medium. There are two types of methods for the heating: one method is to heat the magnetic recording medium by guiding laser light to a recording part via a waveguide, etc. (a direct heating type); and the other method is to heat the magnetic recording medium by converting the laser light to near-field light (a near-field light heating type). The near-field light is a type of electromagnetic field that is formed around a substance. Ordinary light cannot be tapered to a smaller region than its wavelength due to diffraction limitations. However, when light having an identical wavelength is irradiated onto a microstructure, near-field light that depends on the scale of the microstructure is generated, enabling the light to be tapered to a minimal region of approximately tens of nm in size. Since the thermally-assisted recording targets a recording density region that requires selective heating only to the minimal region of approximately tens of nm, the near-field light heating type is preferred.
In U.S. Patent Application Publication No. 2008/205202, a configuration is disclosed in which a near-field-generator is disposed in a front part of a core of a waveguide through which light from a laser diode (LD) propagates.
As a concrete method for generating the near-field light, a method using a so-called plasmon antenna, which is a metal referred to as a near-field light probe that generates near-field light from light-excited plasmon, is common.
Direct irradiation of light generates the near-field light in the plasmon antenna; however, a conversion efficiency of converting irradiated light into the near-field light is low with this method. Most of the energy of the light irradiated on the plasmon antenna reflects off the surface of the plasmon antenna or is converted into thermal energy. The size of the plasmon antenna is set to the wavelength of the light or less, so that the volume of the plasmon antenna is small. Accordingly, the temperature increase in the plasmon antenna resulting from the light energy being converted into the thermal energy is significantly large.
Due to the temperature increase, the volume of the plasmon antenna expands, and the plasmon antenna protrudes from an air bearing surface (ABS), which is a surface facing the magnetic recording medium. Then, the distance between an edge part of the MR element on the ABS and the magnetic recording medium increases, causing a problem that servo signals recorded on the magnetic recording medium cannot be read during the recording process. Moreover, when the heat generation is large, the plasmon antenna may melt.
Currently, a technology is proposed that does not directly irradiate light onto the plasmon antenna. For example, U.S. Pat. No. 7,330,404 discloses such a technology. In this technology, light propagating through a waveguide such as an optical fiber, etc. is not directly irradiated onto the plasmon antenna; however the light is coupled with a plasmon generator in a surface plasmon mode via a buffer portion to excite the surface plasmon in the plasmon generator. The plasmon generator includes a near-field-generator that is positioned on the ABS and that generates the near-field light. At the interface between the waveguide and the buffer portion, the light propagating through the waveguide completely reflects off, and light, which is referred to as evanescent light that penetrates into the buffer portion, is simultaneously generated. The evanescent light and a collective oscillation of charges in the plasmon generator are coupled, and the surface plasmon is then excited in the plasmon generator. The excited surface plasmon propagates to the near-field-generator along the plasmon generator, and then generates near-field light in the near-field-generator. According to this technology, since the light propagating through the waveguide is not directly irradiated to the plasmon generator, an excessive temperature increase of the plasmon generator is prevented.
In U.S. Patent Application Publication No. 2010/103553, a configuration in which a propagation edge is disposed in a plasmon generator that couples to light in a surface plasmon mode is disclosed. The propagation edge has an extremely narrow region, and is for propagating a surface plasmon generated to a near-field-generator that is positioned on an ABS.
Such a thermally-assisted magnetic head must be arranged such that light propagates through a core of a waveguide so as to couple to the plasmon generator that faces the core in the surface plasmon mode. For this, a laser diode (LD) unit including an LD is attached to a slider that is a base of the thermally-assisted magnetic head, enabling laser light to enter into the core. U.S. Patent Application Publication No. 2008/043360 exemplifies a configuration in which an LD unit is attached to a slider.
For the thermally-assisted magnetic head in which the LD unit is attached to the slider as described above, an alignment (light core alignment) of the LD and the core of the waveguide is important in order to guide laser light, which the LD generates, to the plasmon generator by the laser light propagating through the core of the waveguide. When a positional gap between the LD and the core is present, energy loss occurs, causing unnecessary heat generation. As a result, the heat may cause alterations and/or deformations on each part of the slider. Also, since it is necessary for high energy laser light to enter into the core in view of the fact that the loss may occur, the LD needs to generate the high energy laser light, which in turn causes negative effects, such as a short lifetime.
As one example of an alignment method of the core of the thermally-assisted magnetic head and the LD, U.S. Patent Application Publication No. 2009/0059411 discloses a method in which a large number of alignment marks are disposed on an LD unit and/or a slider, and the LD unit and the slider are positioned using the alignment marks. However, since laser light irradiated from the LD of the LD unit is not actually checked, sufficient positional accuracy may not be obtained.
In U.S. Patent Application Publication No. 2008/0056073, a so-called active alignment method is disclosed in which an LD actually generates laser light and a slider and an LD unit are aligned while the light propagating through a core in the slider and emitted from an ABS are monitored with a photo detector positioned facing the ABS. According to this method, the alignment of the slider and the LD unit is performed such that a light coupling efficiency becomes maximum. However, even if the alignment of the slider and the LD unit is performed according to this method, heat application efficiency of a magnetic recording medium may not be sufficient at the time of the thermally-assisted magnetic recording.